The present invention relates to photolytically crosslinkable compositions. More particularly, the present invention relates to such compositions which are photolytically crosslinkable but are thermally stable, that is, not readily subject to crosslinking or vulcanization reactions at temperatures normally encountered under processing conditions. Such compositions find utility as adhesives particularly when blended with tackifiers. In addition, such compositions may be employed to prepare photo printing mats, wherein selective exposure to light results in crosslinking of the composition thereby imparting solvent resistance whereas unexposed and uncrosslinked layers not having such solvent resistance may be later removed during the developing process thereby achieving a flexible surface suitable for printing. In addition, the compositions of the invention may be employed in other suitable applications such as photo resists, photo masking and other applications.
In Canadian Pat. No. 738,500; an ethylene bismaleimide and an N,N'-meta phenylene bismaleimide are disclosed for use as vulcanizing agents in the crosslinking of various unsaturated rubbers including homopolymers and heteropolymers of conjugated dienes, e.g., polybutadiene and butadiene/styrene copolymers, and polyurethane rubbers. Such vulcanizing agents were thermally activated.
In U.S. Pat. No. 3,674,486, photoresist materials comprising a photosensitizer, a crosslinking agent and a rubber-like constituent are disclosed. Suitable crosslinking agents disclosed included multifunctional olefins, such as triallyl cyanurate, pentaerthritol triacrylate, and polyvinyl cinnamate. For the teachings therein, this reference is hereby incorporated in its entirety by reference thereto.
In U.S. Pat. Nos. 4,079,041, 4,163,097, 4,158,730 and 4,158,731 there are disclosed certain organic polymers which can be crosslinked under the action of light having a molecular weight of at least 1,000 and containing as light sensitive groups di-substituted maleimide functionality. The teachings of such patents are also incorporated in their entirety herein by reference thereto.
In U.S. Pat. No. 2,925,407, the curing of high molecular weight substantially unsaturated polymers by the use of free-radical generators such as organic peroxide and free-radical exceptors such as bismaleimide compounds, among others, is disclosed. Such curing operation is thermally activated.
Despite advances in the art utilizing photolytically active curing agents, there remains a desire to prepare compositions that may be photolytically crosslinked but are insensitive to curing prematurely under the action of heat. Compositions which are not thermally stable as previously described, cannot easily be employed in thermal processing operations such as melt extrusion, extrusion coating, melt mixing and other high temperature processes. Alternative techniques such as solvent deposition or other suitable technique must be employed to manufacture and apply thermally sensitive compositions. However, solvents are both expensive and undesirable from the standpoint of atmospheric emissions and combustion hazard. Moreover, thermally unstable compositions and materials prepared therefrom must be subsequently treated in a manner so as to minimize the effects of thermal crosslinking. For example, printing plates that are subject to thermal crosslinking should be maintained at reduced temperatures in order to impart practical lifetimes. Finally, current adhesives used in the preparation of masking tapes and other adhesive products are normally deposited onto a paper stock by solvent casting. The compositions are then partially crosslinked through the use of sulfur vulcanizing agents. This procedure is both cumbersome and difficult to control in a manner to give uniform product properties. Such compositions may also require a paper stock which has been previously pretreated by the use of reactive primers.
It would be desirable to provide a composition which is photolytically crosslinkable but thermally stable which may be prepared, processed, and applied using standard thermal processing techniques.
It would be desirable to provide a composition which is photolytically crosslinkable but thermally stable and which reduces or eliminates the need to use solvents in its preparation or application.